For such dispensers it is expedient when a chamber can be replenished with an inert filler medium during operation, for example, to compensate for a vacuum. One such filler medium, for instance, outside air is, contrary to the non-compressible preparation, mostly compressible. After the chamber has been partly or totally emptied, this filling medium fills the resulting vacant space e.g. by it being drawn by the vacuum into the chamber until pressure has been compensated to equal that of the outside air. Such means are thus particularly suitable for a reservoir chamber which contains a plurality of dispensed amounts of preparation, each one of which is output from the medium outlet on every discharge action by a dispensing unit which may contain a dosing chamber separate from the reservoir chamber. The former is then refilled from the reservoir chamber following each discharge action and then closed off with respect to the reservoir chamber on the subsequent discharge action. As a result, the medium does not flow back into the reservoir chamber, it instead flows to the medium outlet. For this purpose the medium chamber may be pressurized, for example, by its volume being diminished and then re-enlarged for drawing in an amount of the medium to be subsequently dispensed from the reservoir chamber. In the rest or initial position the path of the medium in passing through the dispensing unit from an inlet up to the medium outlet including the medium chamber, is advantageously closed off pressure-tight, so that no air is able to enter into the reservoir chamber or the medium chamber from without.
To prevent the ingress of particles and/or germs when venting the chamber a filter is expediently provided in the venting path. In addition, the reservoir chamber is substantially closed off tight with respect to the outer atmosphere, namely via a sealing seat between the dispensing unit and the reservoir unit. For securing the dispensing unit to the reservoir unit in a rigid position, the sealing faces of this sealing seat are pressed against each other and locked in place. For this purpose an elastically compressible separate sealing unit is disposed between the dimensionally rigid sealing faces of the units. The venting path is then not routed through the internal or housing spaces of the dispensing unit, but is instead provided as a parallel path totally separated from the paths of the medium and also from venting paths which serve to vent such housing spaces of the dispensing unit not subjected to or passed by the medium. Accordingly, the filler medium can only gain access to the chamber to be vented by flowing it through the filter.
The volumetrically variable chamber may also be formed by the reservoir chamber, for example, by a soft squeeze bottle. The neck thereof holds the dispenser unit which comprises the medium inlet permanently communicating with the bottle. As a result, the dispensing unit remains firmly mounted on the reservoir chamber during discharge.